Regional and global changes in cerebral diffusion with normal aging

BACKGROUND AND PURPOSE: We used quantitative diffusion MR imaging to invest igate the microstructural changes that occur in white matter during normal aging in order to identify regional changes in anisotropy and to quantify g lobal microstructural changes by use of whole-brain diffusion histograms. METHODS: Full diffusion tensor MR imaging was performed in 20 healthy volun teers, 20 to 91 years old. Thirteen subjects also underwent high-resolution T1-weighted imaging, so that diffusion images could be coregistered and st andardized to normal coordinates for statistical probability mapping, Relat ive anisotropy (RA) was calculated, as was linear regression of RA with age for each pixel; pixels with a significant correlation coefficient were dis played. For histographic analysis, the average apparent diffusion coefficie nt (ADC) histograms were calculated on a pixel-by-pixel basis. Subjects wer e divided into two equal groups by the median age (55 years) of the populat ion and plotted for statistical comparison. RESULTS: Regional analysis showed statistically significant decreases in RA with increasing age in the periventricular white matter, frontal white mat ter, and genu and splenium of the corpus callosum, despite the absence of s ignal abnormalities on visual inspection of conventional images. Significan t increases in RA were found in the internal capsules bilaterally. ADC hist ograms showed higher mean ADC and reduced peak height and skew in the older age group on group comparisons. CONCLUSION: Quantitative diffusion histograms correlate with normal aging a nd may provide a global assessment of normal age-related changes and serve as a standard for comparison with neurodegenerative diseases.